1. Field of the Invention
This invention relates to a stencil printer, and more particularly to a stencil printer in which a stencil master, which is made by a stencil making section including a thermal head and the like, is wrapped around a printing drum.
2. Description of the Related Art
When thermally making a perforated image on a stencil master while rotating a platen roller in a sub-scanning direction with the stencil master pinched between the platen roller and the thermal head (TPH), the stencil master on which the perforated image has been formed is stored in a storage box utilizing the difference in speed between the conveyor portion on the inlet side of the storage box (a first conveyor portion comprising a master introduction conveyor roller and the platen roller) and the conveyor portion on the outlet side of the storage box (a second conveyor portion comprising a master discharge conveyor roller), i.e., with the conveying speed of the second conveyor portion set lower than that of the first conveyor portion or with the second conveyor portion stopped.
Further when the stencil master is conveyed in order to bring the leading end of the stencil master into engagement with the drum, the portion of the stencil master stored in the storage box is drawn out from the storage box with the second conveyor portion driven at a speed higher than the first conveyor portion, i.e., with the conveying speed of the second conveyor portion set higher than that of the first conveyor portion or with the first conveyor portion stopped, within a range in which no tension is applied to the slack portion of the stencil master.
The conveying speed of the platen roller in the first conveying portion corresponds to the conveying speed of the scanner in the image read-out section which outputs image information to the TPH to cause the TPH to record the image information on the stencil master each time the scanner reads out the image on the original along one line. Since the master introduction roller and the platen roller are driven by the same drive means, the conveying speed of the first conveyor section (the master introduction roller and the platen roller) is governed by the stencil making speed of the TPH. Conventionally the conveying speed of the second conveying portion also corresponds to the stencil making speed of the TPH and substantially the same as that of the first conveying portion though the former is sometimes lower than the latter and sometimes higher than the latter.
However the conveying speed of the second conveyor portion substantially the same as that of the first conveyor portion is too high for conveying the leading end of the stencil master to the clamp mechanism on the drum. That is, the stencil master can slip on the conveyor roller in the second conveying section and the conveyor roller cannot be immediately stopped due to inertia upon stopping the drive means of the second conveyor portion, which results in the leading end of the stencil master overshooting the predetermined position and gives rise to a problem that the leading end portion of the stencil master is curved or bent.
However when the conveying speeds of both the first and second conveyor sections are slowed down, the stencil making time is excessively elongated and convenience in use of the printer deteriorates.